The present invention relates to mass flow measuring apparatus in which fluid is ionized in succession at a particular point of a fluid passage and then detected at a known distance from the ionization point, the elapse of time between the ionization and detection being a measure of the flow rate.
Ionization of fluid is known in the art as an accurate means of measuring mass flow rate if the ionization interval is rapid enough for the changing rate of the fluid flow. Because of the fast response characteristic, such ionization methods are particularly useful for metering input data for accurate control of air-fuel mixture for emission reduction purposes, such as closed-loop controlled internal combustion engines. However, due to the high intensity electric field required for generating corona discharges, electromagnetic radiation is also generated in response to the generation of a corona discharge. This radiation would be sensed as a signal to trigger the measurement if no provisions are made. Furthermore, the electrical signal provided by the charge detecting electrode has a different magnitude and waveshape depending on the flow rate so that the detecting time tends to vary between different waveshapes resulting in an erroneous flow rate measurement.